Various forms of machinery have been used to perform the task of unloading boxes and goods from a conveyor, and stacking them onto a pallet for subsequent transport or storage.
Robot palletizers utilize a stationary pallet table and a robotic arm which is capable of rotating and moving in the vertical direction to deposit boxes and packages in specified orientations on the pallet. Such machines require a relatively large footprint area to take into account the length of the robotic arms. The computer software required to drive such equipment tends to be complicated as one arm is utilized to perform all movements and make all adjustments.
A further difficulty with robot palletizers is that due to the rotating arm, slow movement occurs. This is because the angular momentum of the arm increases with rotational speed and this tends to put undue strain on the components.
A different prior art type is layer palletizers, in which whole layers of goods are shunted together, and then placed on a pallet, which then moves downward. Such an arrangement is limited in packing patterns, and relatively difficult to change between packing patterns and different goods. Additionally, a very large footprint area is required.
Gantry robot palletizers are also known in the prior art, with a gripper means which translates in three dimensions relative to a stationary pallet table. This arrangement is relatively slow, as for some pallet positions relatively large travel is necessary in three dimensions to load the pallet. It also requires the load to be carried at the end of a cantilever, increasing the wear and tear on the device.
A palletizer is described in U.S. Pat. No. 5087169 having a robotic arm which rotates around a pivot mounted upon a carriage, which carriage translates along a substantially H frame track system. The disadvantages of this system stem from the fact that such equipment occupies a large amount of space, and that despite some reduction in footprint, the computational and engineering problems of rotating objects at the end of arms remain. The rotating arms, which can also be articulated, require clear space within which to effectively operate.
The rotating arm produces high torsional loads on the sliding carriage as the load is carried away from the axis of rotation. The machinery to achieve this task is expensive and bulky. It is difficult to achieve a rigid but free moving linear axis when high torsional loads are exerted. Wherever circular movement paths are provided, wasted space results. Because of the rotational effects of the gripper means of prior art devices a rather substantial and extremely positive gripping mechanism needs to be utilized.
U.S. Pat. No. 5051058 discloses a palletizer which requires very complex pallet table movements and an extremely elaborate means to mount boxes onto the pallets. This invention relies on the movement of the pallet, and complex movements prior to being placed on the pallet.
It is an object of the present invention to provide a palletizing system which has a relatively small footprint, yet is capable of a good speed of operation in use.